You’d think so, but maybe not. Anyway it’s something to easily check and eliminate. Car noises are strange, they are often not where you think they are.
If you seem to feel it at the driveshaft area as well as when you accelerate and deaccelerate. Maybe the new JT5 is pivoting up and down and causing a part of the driveshaft to just touch something?
Good luck
It’s laborious but my go to for issues like this is to get 10 ft of plastic tubing. I tape one end at my estimated location of the noise. The other end is in the car and held up to my ear as a stethescope. You have to keep stopping and moving the taped end around to different locations (or get multiple hoses). You basically get to evaluate which hose location gives you the loudest version of the noise you are hearing.
From there, you can target your troubleshooting.
If you are thinking something is pivoting (and I like that suggestion) you can build up lumps of Playdough in key locations and see if it is being pushed out of the way in an excessive manor. The rear of the tranny and the nose of the diff would be my first test points.
What makes me want to dismiss something like the gearbox moving is that the shifter doesn’t move at all. Also, the noise happens even with very little load/torque
Also, all mounts are new (well 2 years and 7k), irs and diff rebuilt etc. car was serviced and inspected before this trip too.
It s not loud. In fact I only started hearing it on Friday when in traffic with cars along side reflecting the sound in Ft Myers going to the JCNA event
One place to look is whether the rear suspension bump stops are being rubbed by the rear tires. Torque of acceleration or deceleration might twist the rear suspension cage a bit and move a tire closer to the bump stop.
I had a noise in an XJ40 that sounded like a scraping noise as and when you describe. Also when I would hit a dip that would cause the car to “bounce” lightly. I could minimize the intensity of the noise by being very gentle on accelerating or decelerating. It sounded a bit like sharpening a knife on a slow speed rotating stone. Ended up being a failed pinion bearing, which was strange when it only had 12,000 miles on the car. The pinion angle was able to change as the suspension varied under load, deceleration and and road. Ended up getting another diff from Coventry West and all was well.
If I recall, I had gotten information from the old forum that led me to make the diagnosis. You might look in there under the XJ40 section. This was late 90s that it had occurred.
It’s a long shot but I would take a look at the waterslingers on the hubs. If they were to rub they would set up quite a racket, as they are virtually a small cymbal!
Finally solved the issue. Didn’t drive it much for the last few months but noise remained until i took it to the shop for a few things. Once on the lift it became clear the rear left wheel has some play. Turned out the splines on the 23 year old / 100k miles Dayton were worn. Wheel hub is good. Other wheels are fine. He swapped it with the spare and no more noise.
I have not only 100k+ miles on these wheels but quite a few track days and autocrosses
The other glitch I had them address were the slow releasing brakes. That was getting worst especially hot. Turned out to be the master. Replaced during the restoration 3 or 4 years ago.
there are spacer that you can add under the rear of the JT5-----could it be that you need to add one----I had to put 2 under mine. Mine was not a scraping noise, more like a banging noise, but, who knows